Multi-mode envelope restoration architecture for RF transmitters

ABSTRACT

An RF transceiver having dual-mode envelope restoration architecture. In narrow-band applications such as GSM/EDGE, a switch-mode amplifier is used to provide an envelope signal for amplitude modulating the phase-modulated signals. To achieve required modulation bandwidth in wide-band applications such as WDCMA, an analog amplifier is used to provide the envelope signal. Furthermore, in the wide-band mode, the envelope modulation is applied through the base of an emitter follower while the collector voltage is scaled to achieve a desired power output in the amplitude-modulated signals.

FIELD OF THE INVENTION

[0001] The present invention is related generally to radio-frequencytransmitters and, more specifically, to envelope restorationtransmitters.

BACKGROUND OF THE INVENTION

[0002] Envelope elimination and restoration (EER) principle is known inthe art. For example, Raab (U.S. Pat. No. 6,256,482 B1) discloses apower-conserving drive-modulation method for EER transmitter, wherein anenvelope baseband component and a phase modulation (PM) radio-frequency(RF) component of a modulated signal are separately amplified and thencombined in a signal for transmission. The major advantage of the EERtransmitter is that the RF PM signal is amplified by highly efficientnonlinear RF amplifiers and the last RF amplifier is amplitude-modulatedby the envelope signal, thereby restoring the modulation at the outputof the transmitter. In Raab, the envelope and phase components areseparated by analog means using a limiter for removing the envelopecomponent such that only the PM component is present at the limiteroutput and an envelope detector is used to detect the baseband componentfrom the original modulated RF waveform. The envelope and phasecomponents can also be generated by a digital signal processor (DSP),which gives better performance over the analog counterpart. As shown inFIG. 1, the envelope component is generated by an envelope modulationmodule 12 in the DSP and D/A converted. After frequency filtering by alow-pass filter F1, the envelope component is changed into a pulse-widthmodulation (PWM) format in a PWM modulator, which feeds a switch-modeclass-D or class-S amplifier A1. The digital PWM signal from theamplifier A1 is converted into an analog signal by a low-pass filter F3.The switch-mode amplifier has higher efficiency than traditional analogamplifiers. The phase component directly modulates a frequencysynthesizer (PLL, F2, VCO). After being amplified by a driver A2, thephase component is amplitude-modulated in a class-E power amplifier A3.

[0003] Alternatively, when the modulation bandwidth is high and therequired PWM frequency is high, which increases losses in the switchingtransistors, it is advantageous to use an analog amplifier A4 to providethe envelope waveform for amplitude modulation, as shown in FIG. 2.

[0004] High-efficiency RF modulation can also be found in McCune (U.S.Pat. No. 6,377,784), which discloses a method of reducing the spreadbetween a maximum frequency of a desired modulation and the operatingfrequency of a switch-mode DC-DC converter.

[0005] Switch-mode envelope modulation is within the limits of presenttechnology of EDGE (Enhanced Data Rates for GSM Evolution). However, theefficiency of switch-mode envelope modulation for use in WCDMA (WidebandCode-Division Multiple Access) is poor due to the high switchingfrequency needed to achieve required modulation bandwidth in WCDMA.Thus, it is advantageous and desirable to provide an enveloperestoration transmitter, which is capable of efficiently transmittingsignals in the GSM/EDGE mode as well as in the WCDMA mode.

SUMMARY OF THE INVENTION

[0006] According to the first aspect of the present invention, there isprovided a transmitter for transmitting information in a modulatedsignal at least in a first carrier frequency band or a second, differentcarrier frequency band. The transmitter is characterized by a signalprocessor for providing baseband data indicative of the information, bymeans, responsive to the baseband data, for providing an envelopewaveform indicative of an envelope of the modulated signal, by

[0007] a phase modulating mechanism for providing a first signal in thefirst carrier frequency band and a second signal in the second carrierfrequency band, by

[0008] a first amplification device, responsive to the envelope waveformand the first signal, for providing the modulated signal in the firstcarrier frequency band, by

[0009] a second amplification device, responsive to the envelopewaveform and the second signal, for providing the modulated signal inthe second carrier frequency band, and by

[0010] a band selection means for selecting at least between themodulated signal in the first carrier frequency band and the modulatedsignal in the second carrier frequency band for transmission, whereinthe first and second signals are phase-modulated radio-frequencysignals, and the first carrier frequency band comprises a first range ofradio-frequencies and the second carrier frequency band comprises asecond range of radio-frequencies lower than the first range.

[0011] Advantageously, the baseband data is provided in a digital form,and the envelope waveform providing means comprises a pulse widthmodulator for providing the envelope waveform for amplitude-modulatingthe second signal.

[0012] Advantageously, the baseband data is provided in a digital form;and the envelope waveform providing means comprises a digital-to-analogconverter for providing the envelope waveform for amplitude-modulatingthe first signal.

[0013] Advantageously, the envelope waveform comprises a first waveformcomponent and a second waveform component, wherein the pulse widthmodulator provides the second waveform component foramplitude-modulating the second signal, and the digital-to-analogconverter provides the first waveform component for amplitude-modulatingthe first signal.

[0014] Preferably, the transmitter further characterized by

[0015] an emitter-follower device (T1) having a collector, an emitterand a base, wherein

[0016] the second waveform component is provided to the collector of theemitter-follower device, and

[0017] the first waveform component is provided to the base of theemitter-follower device, so as to provide an envelope voltage at theemitter for amplitude-modulating the first signal.

[0018] Advantageously, the transmitter is further characterized by

[0019] a power control device for controlling power of the first andsecond amplification devices.

[0020] Advantageously, the second waveform component is scalable so asto achieve a desired output power in the first carrier frequency band.

[0021] According to the second aspect of the present invention, there isprovided a method of envelope restoration for information transmissionin a modulated signal at least in a first carrier frequency band or in asecond different carrier frequency band. The method is characterized by

[0022] providing baseband data indicative of the information, by

[0023] providing an envelope waveform indicative of an envelope of themodulated signal based on the baseband data, by

[0024] providing a first phase modulated signal in the first carrierfrequency band and a second phase modulated signal in the second carrierfrequency band, by

[0025] providing a first amplitude-modulated signal in the first carrierfrequency band based on the envelope waveform and the first phasemodulated signal and a second amplitude-modulated signal in the secondcarrier frequency band based on the envelope waveform and the secondphase modulated signal, and by

[0026] selecting between the first amplitude-modulated signal and thesecond amplitude-modulated signal for transmission.

[0027] Advantageously, the baseband data is provided in a digital form,and the envelope waveform comprises:

[0028] a first waveform component provided by a digital-to-analogconverter for amplitude-modulating the first phase modulated signal forproviding the first amplitude-modulated signal, and

[0029] a second waveform component provided by a pulse width modulatorfor amplitude-modulating the second phase modulated signal for providingthe second amplitude modulated signal.

[0030] Preferably, the envelope waveform comprises a first waveformcomponent provided by a digital-to-analog converter, and a secondwaveform component provided by a pulse width modulator. The method isfurther characterized by

[0031] an emitter follower device having a collector, an emitter and abase, wherein the second waveform component is provided to the collectorof the emitter-follower device, and the first waveform component isprovided to the base of the emitter-follower device, so as to provide anenvelope voltage at the emitter of the emitter-follower device foramplitude-modulating the first phase modulated signal for providing thefirst amplitude-modulated signal.

[0032] Advantageously, the second waveform component is scalable so asto achieve a desired output power in the first amplitude-modulatedsignal.

[0033] According to the third aspect of the present invention, there isprovided a transceiver, adapted to operate at least in a first carrierfrequency band or in a second, different carrier band. The transceivercomprises:

[0034] an antenna,

[0035] a transmitter operatively connected to the antenna fortransmitting signals, and a receiver operatively connected to theantenna for receiving signals, characterized in that the transmittercomprises:

[0036] a signal processor for providing baseband data indicative of theinformation, by means, responsive to the baseband data, for providing anenvelope waveform indicative of an envelope of the modulated signal, by

[0037] a phase modulating mechanism for providing a first signal in thefirst carrier frequency band and a second signal in the second carrierfrequency band, by

[0038] a first amplification device, responsive to the envelope waveformand the first signal, for providing the modulated signal in the firstcarrier frequency band, by

[0039] a second amplification device, responsive to the envelopewaveform and the second signal, for providing the modulated signal inthe second carrier frequency band, and by

[0040] a band selection means for selecting at least between themodulated signal in the first carrier frequency band and the modulatedsignal in the second carrier frequency band for transmission.

[0041] The present invention will become apparent upon reading thedescription taken in conjunction with FIG. 3.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a block diagram showing a prior art envelope restorationtransmitter.

[0043]FIG. 2 is a block diagram showing another prior art enveloperestoration transmitter.

[0044]FIG. 3 is a block diagram showing the multi-mode, dual-bandenvelope restoration transceiver.

BEST MODE TO CARRY OUT THE INVENTION

[0045]FIG. 3 shows a dual-band architecture for a multi-mode enveloperestoration transceiver 10, which comprises a transmitter 100. Thetransceiver 10 has a common antenna 102 for transmitting signals andreceiving signals. The common antenna 102 is split to two differentfrequency bands by a diplexer 104. Transmitter carrier signal isgenerated within a synthesizer PLL1/VCO1. The output frequency of thesynthesizer is divided by 2 by a frequency divider 142 for an upper band(approximately 1900 MHz) and by 4 by a frequency divider 144 for a lowerband (approximately 900 MHz). The lower band can be used for a GSM(Global System for Mobile Communications) or EDGE (Enhanced Data Ratesfor GSM Evolution) mode, while the upper band can be used for a WCDMAmode, for example. As in a prior art envelope restoration transmitter,the modulated signal is divided into an envelope baseband component anda phase modulated radio-frequency (PM RF) component. The PM component216 is generated by a phase modulation module 116 in a digital signalprocessor (DSP) 110. The phase modulation signal 216 is applied to thesynthesizer PLL1/VCO1. Same control bus as for phase modulation 216 isalso used for synthesizer operation frequency programming. For lowerband operations, PM modulated RF signal 244 from the frequency divider144 is fed into an amplifier A5 and further to an amplifier A6, and theamplified signal 344 is conveyed to the transmitter part of a duplexer(F6/F5) and the diplexer 104 to the antenna 102. For the upper band, thePM modulated RF signal 242 is fed to an amplifier A3 and further to anamplifier A4, and the amplified signal 342 is conveyed to thetransmitter part of a duplexer (F4/F3) and the diplexer 104 to theantenna 102. Envelope is restored in amplifier A4 or amplifier A6, whererestoration is carried out by applying variable supply voltage(modulation envelope) to these class-E amplifiers A4, A6.

[0046] The envelope modulation component 210 is generated by a powercontrol and an envelope modulation module 112 in the DSP 110. In EDGEmode (lower band), the envelope modulation component 210 is fed into apulse width modulator (PWM) 120. Digital PWM signal 220 is fed into aswitch-mode amplifier A1 operating either in class-D or class-S.Amplified digital pulses 230 are low-pass filtered in a low-pass filterLP1, which produces analog envelope voltage 250. The analog envelopevoltage 250 is directly fed to a class-E amplifier A6 in the lower bandoperation. In GSM mode, however, the envelope is fixed and depends ondesired output power.

[0047] WCDMA modulation is used in the upper band. For WCDMA modulation,the envelope modulation component 212 generated by the DSP 110 is fed toa digital-to-analog converter 130, which feeds an analog control signal222 to an analog buffer amplifier A2. The amplified envelope signal 232is fed to the base of a transistor T1, which is an emitter follower. Theemitter of the transistor T1 feeds the envelope voltage to the supplyvoltage pin of a class-E RF amplifier A4 and thus restores the envelopeto the PM signal that is amplified within the amplifier A4. At the sametime, the switch-mode envelope modulator (120-A1-LP1) is acting as aswitch-mode voltage regulator, feeding collector voltage 250 fortransistor T1. The collector voltage of the transistor T1 variesaccording to the desired output power. Thus, it is advantageous to keepthis as low as possible within the limit of the linear operation of thetransistor T1. In the arrangement as shown, the collector voltage overT1 is minimized for all WCDMA power levels. Advantageously, when thevoltage over T1 is minimized, the power loss of the analog envelopemodulator output stage T1 is minimized. In contrast, if T1 uses aconstant battery voltage for its collector, the efficiency of the analogenvelope modulator would fall very rapidly for lower power levels.

[0048] The transmitter band of operation is selected by a band selectionmodule 114 using signals BS1, BS2, which enable the desired transmitterblock. Amplifiers A3, A5 are used to provide drive signals on anappropriate level for the corresponding class-E amplifiers A4, A6. Onlow transmit power levels, it is advantageous to reduce the drive signallevel in order to reduce PM-modulated RF signal feed-through viaamplifiers A4 and A6. As shown in FIG. 3, a digital-to-analog converter132 is used to change the input drive according to the desired outputpower based on digital signals 214 provided by the power control andenvelope modulation module 112. If the same RF drive level is used forall output power levels, the PM-modulated RF signal feed-through wouldbe too high on low power levels and thus reduce the dynamic range of theamplitude modulated class-E amplifiers. In the upper band WCDMAoperation, driver A3 also gets its supply voltage from the switch-modemodulator (120-A1-LP1), which reduces current consumption of the driverA3.

[0049] The receiver section of the transceiver 10 consists of a two-banddirect conversion receiver 150. Front-end filters for the upper andlower bands are F3 and F5. Local oscillator signal is generated withinsynthesizer PLL2/VCO2 based on frequency control signal 218 provided bythe phase modulation and frequency control module 116. Depending on theselected frequency band, the output signal from VCO2 is divided eitherby 2 by a frequency divider 146 or by 4 by a frequency divider 148.Divider outputs 246, 248 provide phased LO signals for the receiver Iand Q mixers. The receiver 150 has common baseband I and Qfilters/amplifiers (not shown). Filter corner frequency is changedaccording to the received signal modulation (GSM/EDGE or WCDMA).Advantageously, baseband amplifiers in the receiver 150 also contain anautomatic gain control (AGC) function. The receiver I and Q signals 152,154, after being analog-to-digital converted by corresponding converters136 and 138, are processed by a module 118 in the DSP, which alsoprovides an AGC function and an automatic frequency control (AFC)function. Digital-to-analog converted AFC signal from D/A converter 134is fed to a voltage controlled temperature compensated crystaloscillator (VCTCXO), which acts as a common reference for thesynthesizers (PLL1/VCO1, PLL2/VCO2).

[0050] It should be noted that in the transceiver 10, as illustrated inFIG. 3, the EDGE modulation is associated with the lower band. However,if EDGE modulation is needed on the upper band, envelope modulation canbe generated either using the analog modulator T1 (with variable supplyvoltage generated by A1-LP1) or the switch-mode modulator A1-LP1 (withtransistor T1 being driven into saturation by the D/A converter 130.

[0051] The present invention can be applied to transceivers having threeor more frequency bands such that each frequency band may have its ownsynthesizer PLL/VCO. Alternatively, two or more bands share a commonsynthesizer with each band having a different frequency divider.Furthermore, in the transceiver 10, as illustrated in FIG. 3, the outputof the transmitter VCO1 is frequency divided by 2 for the upper bandoperation and by 4 for the lower band operation. However, the outputfrequency of the transmitter VCO1 can be directly used for the upperband and divided by 2 for the lower band. This arrangement would reducethe current consumption. However, the VCO pulling problem will be worseon the upper band due to its own transmit signal. The arrangement inwhich the envelope signal is fed to the base of transistor T1 while theswitch-mode envelope modulator 120-A1-LP1 acts as a switch-mode voltageregulator feeding collector voltage for T1, can also be used in atransceiver having only one band. The advantage of using thisarrangement is that the power losses of the analog envelope modulator130-A2 can be minimized when the voltage over T1 is minimized.

[0052] The tranceiver of the present invention has been described ashaving a lower band and an upper band. It should be understood that inthe tranceiver with a dual-mode envelope restoration architecture,according to the present invention, the switch-mode amplifier is usedgenerally to provide an envelope signal for narrow-band applicationswhile the analog amplifier is generally used to provide the envelopesignal for wide-band applications. Accordingly, in the wide-bandapplication, the envelope modulation is applied through the base of theemitter follower (T1) while the collector voltage is scaled to achieve adesired power output in the amplitude-modulated signals.

[0053] Although the invention has been described with respect to apreferred embodiment thereof, it will be understood by those skilled inthe art that the foregoing and various other changes, omissions anddeviations in the form and detail thereof may be made without departingfrom the scope of this invention.

What is claimed is:
 1. A transmitter (100) for transmitting informationin a modulated signal at least in a first carrier frequency band or asecond, different carrier frequency band, said transmitter characterizedby a signal processor (112) for providing baseband data (210,212)indicative of the information, by means (120,130), responsive to thebaseband data, for providing an envelope waveform (232, 250) indicativeof an envelope of the modulated signal, by a phase modulating mechanism(116, PLL1, VCO1, 142, 144) for providing a first signal (242) in thefirst carrier frequency band and a second signal (244) in the secondcarrier frequency band, by a first amplification device (A3, A4),responsive to the envelope waveform (232, 250) and the first signal(242), for providing the modulated signal (342) in the first carrierfrequency band, by a second amplification device (A5, A6), responsive tothe envelope waveform (250) and the second signal (244), for providingthe modulated signal (344) in the second carrier frequency band, and bya band selection means (114) for selecting at least between themodulated signal in the first carrier frequency band and the modulatedsignal in the second carrier frequency band for transmission.
 2. Thetransmitter of claim 1, characterized in that the first and secondsignals are phase modulated radio-frequency signals.
 3. The transmitterof claim 2, characterized in that the first carrier frequency bandcomprises a first range of radio frequencies and the second carrierfrequency band comprises a second range of radio frequencies lower thanthe first range, that the baseband data (210, 212) is provided in adigital form, and that the envelope waveform providing means (120, 130)comprises a pulse width modulator (120) for providing the envelopewaveform for amplitude-modulating the second signal.
 4. The transmitterof claim 2, characterized in that the first carrier frequency bandcomprises a first range of radio frequencies and the second carrierfrequency band comprises a second range of radio frequencies lower thanthe first range, that the baseband data (210, 212) is provided in adigital form, and that the envelope waveform providing means (120, 130)comprises a digital-to-analog converter (130) for providing the envelopewaveform for amplitude-modulating the first signal.
 5. The transmitterof claim 4, characterized in that the envelope waveform providing means(120, 130) further comprises a pulse width modulator (120) for providingthe envelope waveform for amplitude-modulating the second signal.
 6. Thetransmitter of claim 5, characterized in that the envelope waveform(232, 250) comprises a first waveform component (232) and a secondwaveform component (250), wherein the pulse width modulator (120)provides the second waveform component for amplitude-modulating thesecond signal.
 7. The transmitter of claim 5, characterized in that theenvelope waveform (232, 250) comprises a first waveform component (232)and a second waveform component (250), wherein the digital-to-analogconverter (130) provides the first waveform component foramplitude-modulating the first signal.
 8. The transmitter of claim 5,characterized in that the envelope waveform (232, 250) comprises a firstwaveform component (232) and a second waveform component (250), whereinthe digital-to-analog converter (130) provides the first waveformcomponent, and the pulse width modulator (120) provides the secondwaveform component, said transmitter further characterized by anemitter-follower device (T1) having a collector, an emitter and a base,wherein the second waveform component (250) is provided to the collectorof the emitter-follower device, and the first waveform component (232)is provided to the base of the emitter-follower device, so as to providean envelope voltage at the emitter of the emitter-follower device foramplitude-modulating the first signal.
 9. The transmitter of claim 8,characterized in that the second waveform component (250) is scalable soas to achieve a desired output power in the modulated signal (342) inthe first carrier frequency band.
 10. The transmitter of claim 1,further characterized by means (112, 132) for controlling power of thefirst and second amplification devices.
 11. The transmitter of claim 3,characterized in that the first carrier frequency band comprises afrequency band substantially at 1900 MHz.
 12. The transmitter of claim3, characterized in that the second carrier frequency band comprises afrequency band substantially at 900 MHz.
 13. The transmitter of claim 3,characterized in that the first carrier frequency band comprises afrequency band substantially at 1900 MHZ for wideband code-divisionmultiple access applications, and the second carrier frequency bandcomprises a frequency band substantially at 900 MHz for GSMapplications.
 14. A method of envelope restoration for informationtransmission in a modulated signal at least in a first carrier frequencyband or in a second different carrier frequency band, said methodcharacterized by providing baseband data (210, 212) indicative of theinformation, by providing an envelope waveform (232, 250) indicative ofan envelope of the modulated signal based on the baseband data, byproviding a first phase modulated signal (242) in the first carrierfrequency band and a second phase modulated signal (244) in the secondcarrier frequency band, by providing a first amplitude-modulated signal(342) in the first carrier frequency band based on the envelope waveformand the first phase modulated signal and a second amplitude-modulatedsignal (344) in the second carrier frequency band based on the envelopewaveform and the second phase modulated signal, and by selecting betweenthe first amplitude-modulated signal and the second amplitude-modulatedsignal for transmission.
 15. The method of claim 14, characterized inthat the baseband data is provided in a digital form, and that theenvelope waveform comprises: a first waveform component provided by adigital-to-analog converter (130) for amplitude-modulating the firstphase modulated signal for providing the first amplitude-modulatedsignal, and a second waveform component provided by a pulse widthmodulator (120) for amplitude-modulating the second phase modulatedsignal for providing the second amplitude modulated signal.
 16. Themethod of claim 14, characterized in that the baseband data is providedin a digital form, and that the envelope waveform comprises a firstwaveform component provided by a digital-to-analog converter, and asecond waveform component provided by a pulse width modulator, saidmethod further characterized by an emitter follower device (T1) having acollector, an emitter and a base, wherein the second waveform componentis provided to the collector of the emitter-follower device, and thefirst waveform component is provided to the base of the emitter-followerdevice, so as to provide an envelope voltage at the emitter of theemitter-follower device for amplitude-modulating the first phasemodulated signal for providing the first amplitude-modulated signal. 17.The method of claim 16, further characterized in that the secondwaveform component is scalable so as to achieve a desired output powerin the first amplitude-modulated signal.
 18. A transceiver (10) adaptedto operate at least in a first carrier frequency band or in a second,different carrier band, comprising: an antenna (102), a transmitter(100) operatively connected to the antenna for transmitting signals, anda receiver (150) operatively connected to the antenna for receivingsignals, characterized in that the transmitter comprises: a signalprocessor (112) for providing baseband data (210,212) indicative of theinformation, means (120,130), responsive to the baseband data, forproviding an envelope waveform (232, 250) indicative of an envelope ofthe modulated signal, a phase modulating mechanism (116, PLL1, VCO1,142, 144) for providing a first signal (242) in the first carrierfrequency band and a second signal (244) in the second carrier frequencyband, a first amplification device (A3, A4), responsive to the envelopewaveform (232, 250) and the first signal (242), for providing themodulated signal (342) in the first carrier frequency band, a secondamplification device (A5, A6), responsive to the envelope waveform (250)and the second signal (244), for providing the modulated signal (344) inthe second carrier frequency band, and a band selection means (114) forselecting at least between the modulated signal in the first carrierfrequency band and the modulated signal in the second carrier frequencyband for transmission.